Hitherto, a transistor (TR)-based biosensor having a structure that includes a transistor has been mainly used among sensors that detect biomolecules using an electrical signal. The biosensor is manufactured by using a semiconductor process and has advantages in that conversion into an electrical signal is fast and a combination of an integrated circuit (IC) and microelectromechanical systems (MEMS) is easily achieved. Therefore, many researches have been conducted on the biosensor.
As an essential patent about measuring a biological reaction using a field-effect transistor (FET), there is U.S. Pat. No. 4,238,757 applied in 1980. This relates to a biosensor measuring a change in a semiconductor inversion layer due to a change in surface charge density in an antigen-antibody reaction as a current and relates to protein among biomolecules.
In U.S. Pat. Nos. 5,466,348 and 6,203,981, contents about improving a signal-to-noise ratio (S/N ratio) using a thin-film transistor (TFT) and combining a circuit is disclosed. However, in order to solve disadvantages of the biosensor using an FET manufactured by the semiconductor process, a biosensor using a thin-film transducer is disclosed.
US Patent Publication No. 2004/0211251 discloses a thin-film transducer type sensor.
The thin-film transducer type sensor uses mechanical stress of a thin-film membrane due to a chemical or biological reaction that occurs in a thin-film connected to an electrode such as gold. That is, a change in capacitance is measured by a change in the distance between the thin-film deformed by the mechanical stress due to the chemical or biological reaction and a lower electrode (this corresponds to a change in the distance between two electrodes), and an analyte is detected from the measured change in capacitance.
FIG. 1 is a conceptual diagram of a thin-film transducer disclosed in U.S. Pat. No. 7,086,288. A thin-film surface of the left is treated for a bond with a biomolecule, and a change in capacitance occurs when a biomolecule is bonded thereto.
Here, the change in capacitance includes, in addition to the bond with a biomolecule, an effect of a pressure applied from the outside. In U.S. Pat. No. 7,086,288, a reference thin-film structure is further provided on the right to compensate for the effect of the pressure applied from the outside. Accordingly, the principle that the difference between a change in the capacitance of the thin-film on the left and a change in the capacitance of the thin-film on the right is the same as the difference in the capacitance due to the bond with a biomolecule is used.
In a case of this structure, manufacturing cost of the transducer is increased, an additional system for the difference in capacitance has to be provided, resulting in problems of the complexity of the entire structure, increase in cost, and the like.